The Conservatives have accused teaching unions of damaging school sport by
banning teachers from supervising pupils outside of class time.

They claimed that the NASUWT, the biggest teaching union, had issued guidance to teachers saying: “Members should refuse to attend any meetings and activities outside school session times which are not on the school calendar and which are not within directed time.”

The union instructed its members in December 2011 to take action short of industrial action as part of a dispute with the Education Secretary over pay, workload and pensions. The instructions remain in place.

The NUT was said to be balloting its members to join the NASUWT in a “work to rule”.

Damian Hinds, a Conservative member of the Education Select Committee, said: “Following the huge success of the Olympics, the last thing we want is to go back to a time when school sport was crippled by militant union leaders embarking on a damaging and irresponsible work to rule.”

"It is utterly hypocritical for the unions to blame the government for a lack of sport in school at the same time as ordering their members not to help with activities outside of school hours."

But Chris Keates, General Secretary of the NASUWT, said the Conservatives had been “selectively quoting”. She added: "The NASUWT action short of strike action has not targeted sporting activities at all.

"The sport saboteurs are not unions, but ideologically driven Government ministers who are vandalising our education service."